I don't think this is correct. Judges regularly have to get their heads around all sorts of very abstruse areas of knowledge, whether it's in medicine, or engineering, or IT, or construction, or accounting practice, or aeronautics or, well, anything. They deal with medical issues particularly frequently in various different areas of the law. If medics can't explain medical concepts adequately so judges can understand them, how can they expect lay people to?
I don't think the issue here is that the judges were reluctant to say that, in lay people's terms, that Archie is dead. If anything, the reluctance lay with the medics, and for good reason: they have a clearly laid down protocol for testing brain stem death which is fine for 99.999% of cases, it's simply that in this one case it wasn't because Archie had deteriorated too far. So they were unable to tell the courts that he was brain stem dead, and the courts understandably said they weren't going to override the medics on that one.